Photoelectric system



Ward! 1959 D. J. MlNDHElM 2,878,395

PHOTOELECTRIC SYSTEM filed July 16, 1956 3 Sheets-Sheet 1 I March 17, 1959 D. .1. MINDHEIM PHOTOELECTRIC SYSTEM 3 Sheets-Sheet 2 Filed July 16, 1956 mom PDnFDO INPUT March 17, 1959 Filed July 16, 1956 D. J. MINDHEIM PHOTOELECTRIC SYSTEM 3 Sheets-Shet 5 VOLT METER FIG. 3

2,878,395 PHOTOELECTRIC SYSTEM Daniel I. Mindheim, Glen Cove, N. Y., assignor to Llndly 8.: Company, Inc., Nassau County, N. Y., a corporation of New York Application July 16, 1956, Serial No. 598,088

6 Claims. (Cl. 250-419) The present invention relates to a photomultiplier system and is directed particularly to obtaining uniform signals from such systems despite varying conditions during operation. Photomultipliers are useful in many applications where it is desired to convert a visual or light signal into an '20 electrical signal. An example of such use is in apparatus for inspecting textile yarns and other materials forming" the subject matter of a United States patent application filed by Howard C. Lindemann and Daniel J. Mindheim on July 17, 1956, Serial Number 598,364. In such apparatus the material'to be inspected passes through a light beam directed between a light source and thephoto tube, a suitable optical system being provided to define the beam and direct it on the cathode of the tube. Ari

interruption or sudden variation in the light received by the phototube produces a signal pulse which is amplified and used to actuate any desired mechanism, for example to stop the material and/or to provide a visual, audible, 1

electrical or other signal as desired.

However, the use of photomultipliers has heretofore ciently uniform and stable under conditions encountered in use to give satisfactory results. For example, in the above mentioned yarn inspecting apparatus, the amount of light impinging on the cathode of the phototube may be decreased by dirt or lint collecting on the envelopes of the lamp and the phototube and on the lenses or other The light may also be elements of the optical system. varied by variations in the voltage supply of the lamp and by deterioration of the lamp in use. Moreover, changes occur in the characteristics of the phototube itself due,

for example, to changes in temperature or to the progressive decay of the tube.

tofore been sufficiently stable for many applications where they might otherwise be useful.

It is an object of the inventionto provide a photomultiplier system that is highly sensitive and is nevertheless highly stable in the sense that under all operating 3 the envelopes of the phototube and lamp and on elements 3 of the optical system. apparatus, the system in accordance with the invention also makes it possible to inspect yarns of different sizes without modifying the equipment. Such apparatus using a photomultiplier system in accordance with thepresent invention adjusts itself automatically to accommodate yarns of different sizes without affecting the selected value of the signalpulse producedby agiven dcfect in the 7 Other objects and advantages of the invention will been limited by the fact that their operation is not suifi- Because of these factors it affecting their operation, photomultipliers have not here- As applied to yarn inspecting appear from the following description and claims in conjunction with the accompanying drawings whichillustrate by way of example one embodiment of the invention and in which:

Figs. 1 and 2lare togethera wiringdiagram of. a photomultiplier and control system in accordance with the invention.

Fig. 3 is'.a wiring diagram of an amplifier for ampliw tying the signal .ofthe photomultiplier, and

Fig. 4 is a schematic plan of yarn inspecting apparatus: .utilizing a photomultiplier: system 1 in accordance with the. invention. 3

The embodiment of the invention illustrated by way of example in. the drawings comprises a phototube 1,? a lampZ arranged to direct a beam of light on the 5 phototube, a mainpower supply unit 3, a second power 1 supply'unit 4 to. the supply power to the lamp, a control circuit 5 for controlling the light output of the lamp in accordance with the output-of the phototuhe and an amplifier 6 (Fig. 3) for amplifying a signal from the J phototube for use in controlling equipment or in operat- To illustrate one'of manyapplications of invention there is shown schematically in Fig. 4, an arrangement for inspecting ing a visual,.audible or electrical signal.

a sheet. of yarns. In thearrangement shown, a beam oft-light from the lamp 2 is directed on the phototube. 1 by a suitable optical system 7 which has been indicated w schematically as lenses, though it will be understood that t suitable optical elements are used to define a beam of the desired characteristics, for example-a beam of parallel "rays. The material M that is to be inspected is shown as a plurality of yarns which are supplied for example r from individual spools or cones and are wound onto a rotating reel 8. In passing from the supply to the reel 8, the yarns pass over and under suitable guide bars 9 which guide the yarns-so that they pass across the beam of. light directed by the lamp and optical system 7 onto the phototube 1. As long as the yarns are free from defects, 1 they intercept a constant amount of light so that the output of the phototube 1 has a predetermined steady 1 value. However, any projecting portions of fibers on the yarns will intercept more light andthereby momentarily change the output of the'phototube'to produce a signal.

whichis suitably amplified by the: amplifying circuit 6 and used for example to stop the reel 8 or to produce However, this gives rise tothe difiiculty that the correct functioning of the tube may be impaired by lint, dust or dirt collecting on theenvelopeof the phototube 1 or lamp 2 or on elements of the optical system 7. Moreover, the phototube-is affected by other factors such as temperature variation and progressive aging of the tube and of the lamp. In accordance with the invention, these difficulties are overcome by controlling the light output of the lamp sothat the normal or steady output of the I phototube is maintainedat a predetermined optimum value.

The phototube 1 is a photomultiplier having a cathode .11, anode 12 and a plurality of dynodes 13. The cathode 1-1 is connected by a suitablelead 14 to terminal A of a plug '15 through which a high negative voltage, for example-"minus 590 volts, is supplied to the cathode from I the power supply circuit described below. The dynodes 13 are connecte to the lead 14 through a series of resistances 15 in the manner shown (Fig. 2) so that the 1 negative voltages applied to the dynodes are successively. Inthe operation of the tube, electrons emitted by the cathode'when lightstrikes it are directed 1' tothe first dynode where theyproducemore electrons of lower value.

by secondary emission. These electrons are directed to Patented -M-ar.17-, a,

the second dynode and produce a still larger number of tube 50 is connected by leads 33" to a source of current electrons which are directedto the third dynode. This a d. also onne t d through n sers 59 to ground. is continued through the entire series of dynodes. The The anode of the tube 50 and the last mentioned grid of the cathode so as to Obtain a much hi her current 15 gh which y are connected o t ircuit 5 value than would otherwise be obtained The photo for controlling the intensity of the lamp 2, as described tube 1; is: provided with a shield 16 connected through belowa high resistance 17 to the lead 14. The shield is pro- The lamp control circuit comprises the resistance 25 vided with a suitable window for transmission of light gand a trl'ede 205, the g of Which is onfrom the lamp to the phototube; nected through resistances 61 and 62 to the anode 12 of The anode 12 of the photomultiplier tube 1 is conphototube I. The grid is also connected through remlnal E of plug 15 through which B+ voltage isapthe resistance 25 so that the voltage between the grid lied to the plate The cathode of the trtode A is 15 and ath f b 203 p s on the IR drop In connected by a lead 22 to an output plug 23 The ansistance 25 and hence on the steady current of the photoode/12 of the phototube 1 is. also connected by a lead tube 1. The anode of tube 208 is connected through a 24. through a resistance 25 and microammeter 26 to Plate resistance 64 and lead 21 to terminal E of P 15 ground or other reference point of predetermined popp y g Voltage and i connected y lead 65 0 tentiaL. It will be understood that the'current flowing 20 te mi al B Of plug 15- This terminal is connected by a.

as: well'as on other factors such as temperature, extent denser 63 t0 ground-t A Selected Positive voltage is P- of deterioration of the tube, etc. The condenser 18 plied to the Cathode 0f the "lode 67 by a Potentiometers blocksthe fl f t d current f m anode 12 f 25 69 connected to a lead 70 to which a constant positive the: phototube to th grid of the triode 20A. However, g for example 250 volts, 1s pn by the p w when there is a' suddentchange incurrent produced for. pp y circuit described above The amide of e 67 example f r momentary i t ti f li ht f th is connected by a lead 71 to the control grid of a tetrode lamp 2,v the resulting pulse is transmitted through. the which grid is also connected through a rcslstancc 3 condenser 18.- to. the grid of tube 20A which acts as a 30 to the positive voltag s pp y d 70. Theanode of output 23. p I former 31 while the other lead is connected through a" Thepower supply 3 (Fig.- 1)'operates from a s it bl leakage resistance 7;? to the second grid of the tube. The source, for example 110 volt A. C. mains 30, and supcathode of tube 72 is connected by a lead 6th: to terrn1- plies regulated. voltages of constant value to the several 1181 Of t e plug 15 and hence to the anode of tube components of the equipment as required. The power 50 u. o the osclllatot supplying current to he supply circuit is shown as comprisingatransformer 31, p D t theprimary ofwhich is, con e t d th ou h a it h 32 In the control circuit, trlodes 20B and 67 act as D. C. with the supply mains 30. The secondary of the transamplifiers to mplify the volta appearing aflross the former is provided with a plurality'of taps to furnish reslstauce 25 y ea on of the IR drop resulting from the various voltages that are required. Leads 33' are the steady en put of the phototube 1 while the connected to terminal C d I) f; plug 15 d id tetrode 72 acts as a variable resistance controlling the 6 3 volt current to heaters for various tubes Leads 34 pp y of POWer from the osclllatef Circuit 4 t0 the lam supply 6 volt current to the heaters of tubes 37 and 38. for y reason, the anode of the phototubc nds to nected to th cathode ofth phototube 1; A f h anrincrease'in the IR drop across the plate resistance 64 circuit comprising transformer'secondary leads 40, tubes and a the p f volhage 0f the tube This 3 41 and 42 and gashhed diodes 43 with the conneclower voltage 18 transmitted directly to the grid of tube tions and associated components shown in the drawings 67 (Flg 1) causmg a decrease In the current flow through The lamp 2 (Fig. 2) is shown as an incandescent lamp having a filament 45, one end of which is connected by grid of tube 72 a lead 4 to groundwhxle the other end ls chmnectedby raising-the voltage supplied to the oscillator circuit 4 a h 47 to the lamp f supply power through leads'60 and a.- The R. F. output of the oscil- Ply 4 shown as an Oscillator supplying radio fletquency lator to the lamp 2 is thereby increased with a resulting current to the lamp 2. It comprises a tetrode 50 and an increase i h i h Output of h l Thus a oscillatorcoil 51 having g and crease in the-current of phototube 1 results automatically One end of the winding 51c-is grounded whilethe other int-increasing the. light output of the lamp 2 which in is connected by lead 47 to the-filament 45 of lampfth a turn increases the current of the phototube 1 to bring One end of the winding 51a is connected by lead 52 to it back to the selected level. The potentiometer 69 prolead 53 and throu h a resistance 54 and condenser 55, value The top limit for the lamp is controlled by the arranged in parallel-with one another, to a grid of tube cut-off point of the tube 67.

50. A condenser 56 is connected in parallel across the The output terminal 23 of the phototube circuit is conwinding 51a. One end of the winding 51b. is connected nected as desired to an external circuit to which it is by lead 52 to the cathode of tube-50"while the otherend desired to transmit a signal pulse resulting from mois grounded' and isconnected throughsalead -57 and-con mentary interruption or diminution of light falling on' denser'SS to theother'grid oftube-5th Theheater-of the phototube, for example by reason of a defect in material being inspected. As illustrated by way of example in Fig. 3, the ouput plug 23 is connected through a mating plug 23' and a potentiometer 75 to an amplifier 6 comprising tubes 81, 82, 83 and 84 together with the associated components and connections shown in the drawings. The output of the amplifier circuit controls a relay 85 having operating contacts 86 and 87. As illustrated in the drawing, the contact 86 controls an output 88 adapted to be connected to any device which it is desired to control, for example a stop-motion for the reel 8 of the inspecting mechanism shown by way of example in Fig. 4. The contact 87 is shown connected to a counter 89 to record the number of operations. It will be understood that the amplified output of the phototube 1 may be used to operate signal or any other device as desired. The output circuit comprising the cathode follower A and the amplifier 6 is responsive to signal pulses emitted by the phototube by reason of a momentary interruption or diminution of light falling on its cathode. The light control circuit, on the other hand, acts as an integrating circuit, the effect of pulses being damped out by the circuitry shown and particularly by the condenser 68 in the grid circuit of the control tube 67. Hence the light control circuit is not responsive to signal pulses but rather to the steady or integrated current output of the phototube 1. The light output of the lamp 2 is thereby automatically and precisely controlled to maintain the steady current output of the phototube at a constant value.

By reason of theextreme sensitivity required in order for the apparatus to respond to a single filament or fibre, the available margin between electrical noise in the circuit and a signal pulse is extremely small. The light control circuit in accordance with the invention makes it possible to operate in this small margin despite deterioration of the phototube or lamp or other factors such as the optical system becoming dirty. Satisfactory operation of the apparatus over a long period of time is thereby assured.

While a preferred embodiment of the invention has been shown in the drawings and particularly described the invention is in no way limited to this embodiment but is susceptible of modification and variation within the scope of the appended claims.

What I claim and desire to secure by Letters Patent is:

1. In apparatus for inspecting material, a sensitive photoresponsive element, the electrical conduction of which varies with small variations in the amount of light falling on said element, means for supplying a constant direct current potential, 2. primary circuit comprising said photoresponsive element and potential supplying means connected to supply a constant potential to said element, an electrical lamp, means directing light from said lamp onto said photoresponsive element to induce a flow of current through said element, said current de' creasing with a decrease of light on said element, means for passing material to be inspected through the path of said light so that a momentary variation in said material causes a variation in the light received by said photoresponsive element and a corresponding variation in the current flowing through said element to produce a signal pulse, an output circuit responsive to pulses, means connecting said photoresponsive element to said output circuit to transmit a signal pulse to said output circuit, means supplying current to said lamp, and a light control circuit for varying the current supplied to said lamp and thereby controlling the light emitted by said lamp, said light control circuit comprising an integrating circuit connected to said primary circuit, said integrating circuit being responsive to steady current flowing through said photoresponsive element but not responsive to signal pulses and means controlled by said light control circuit to increase the current supplied to said lamp upon decrease of the steady current flowing through said photoresponsive element to maintain the current of said element at a constant value except for said signal pulses.

2. Apparatus according to claim 1, in which said output circuit is reactively coupled with said primary circuit.

3. Apparatus according to claim 1, in which said primary circuit comprises a resistance connected in series with said photoresponsive element and said potential supply means and in which said light control circuit is connected across said resistance.

4. In apparatus for inspecting material, a photomultiplier tube having a cathode, anode and a series of dynodes, power supply means for maintaining a constant potential difference between said cathode and anode and lesser potential differences between successive dynodes of said series, an electric lamp having a light output varying with current supplied to said lamp, means directing light from said lamp onto said tube to excite said tube and thereby produce a flow of current through said tube, said current decreasing with a decrease of light falling on said tube, means for passing material to be inspected through the path of said light so that a momentary variation in said material causes a variation in the light received by said phototube and a corresponding variation in the current flowing through said phototube to produce a signal pulse, an output circuit responsive to pulses, means coupling said phototube to said output circuit to transmit a signal pulse to said circuit, means supplying current to said lamp, and a light control circuit for varying the current supplied to said lamp, said light control circuit comprising an integrating circuit connected to said phototube, said integrating circuit being responsive to steady current flowing through said phototube but not responsive to signal pulses and current varying means controlled by said light control circuit to increase the current supplied to said lamp upon decrease of the steady currentthrough said phototube to maintain the current through said phototube at 'a constant value except for said signal pulses.

5. Apparatus according to claim 4, in which said means supplying current to ,said lamp comprises a radio frequency oscillator having its output connected to said lamp.

6. Apparatus according to claim 4, in which said current varying means comprises a variable resistance tube having a grid connected to said light control circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,906,441 Alexanderson et al. May 2, 1933 2,477,646 Perlow et al. Aug. 2, 1949 2,801,342 Jones July 30, 1957 2,850,664 Parsons Sept. 2, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,878,395 March 17, 1959 Daniel J. Mindheim It is herebfi certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 64, list of references cited, for

"2,8850,664 Parsons----- Sept. 2 1958 read 2,850,644 Parsons--- Sept. 2, 1958 Signed and sealed this 14th day of July 1959 (SEAL) Attest:

KARL H.. AXLINE ROBERT C. WATSON Attesting Oflicer I Commissioner of Patents 

